Implementing buried fet below and beside finfet on bulk substrate

ABSTRACT

A method and circuit for implementing an enhanced transistor topology enabling enhanced current capability with added device drive strength with buried field effect transistors (FETs) below and beside a traditional FinFET on a bulk substrate, and a design structure on which the subject circuit resides are provided. Buried field effect transistors (FETs) are formed on either side and under the traditional FinFET. The gate of the FinFET becomes the gate of the parallel buried (FETs) and allows self alignment to the underlying sources and drains of the buried FET devices in the bulk semiconductor.

FIELD OF THE INVENTION

The present invention relates generally to the data processing field,and more particularly, relates to a method and circuit for implementingan enhanced transistor topology enabling enhanced current capabilitywith added device drive strength with a buried field effect transistor(FET) below and beside traditional FinFETs on a bulk substrate, and adesign structure on which the subject circuit resides.

DESCRIPTION OF THE RELATED ART

Fin-type field effect transistors (FinFETs) are high speed devices thatcan be densely packed on a substrate. FinFETs offer relatively highcurrent density transistors but limitations still drive designs toutilize a large number of FinFET fingers to drive large capacitanceloads both on die and particularly off die.

A need exists for a method and circuit for implementing an enhancedtransistor topology enabling added device drive strength with a buriedfield effect transistor (FET) below and beside traditional FinFETs on abulk substrate, for example, increasing current densities per fin andper unit area of transistor.

SUMMARY OF THE INVENTION

Principal aspects of the present invention are to provide a method andcircuit for implementing an enhanced transistor topology enablingenhanced current capability with buried field effect transistors (FETs)below and beside traditional FinFETs on a bulk substrate, and a designstructure on which the subject circuit resides. Other important aspectsof the present invention are to provide such method, circuit and designstructure substantially without negative effect and that overcome manyof the disadvantages of prior art arrangements.

In brief, a method and circuit for implementing an enhanced transistortopology enabling enhanced current capability with buried field effecttransistors (FETs) below and beside a traditional FinFET on a bulksubstrate, and a design structure on which the subject circuit residesare provided. Buried field effect transistors (FETs) are formed oneither side and under the traditional FinFET. The gate of the FinFETbecomes the gate of the parallel buried (FETs) and allows self alignmentto the underlying sources and drains of the buried FET devices in thebulk semiconductor.

In accordance with features of the invention, a traditionalsemiconductor FinFET is formed via traditional FinFET processing andincludes forming the FinFET gate, gate dielectric and depositing ablanket spacer film via traditional FinFET processing. The traditionalsource and drain implants are utilized to dope not only the FinFETsources and drains but also the new buried transistor sources and drains(S/D) diffusions. These areas exist on either side of the FinFET gatematerial that exists on the sides of the semiconductor fin. Theimplanted regions are activated via the same anneal or anneals as thebase FinFET.

In accordance with features of the invention, process flow issubstantially the same as an existing FinFET process flow with onlypredefined layout shape changes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIGS. 1, 2, 3, 4, and 5 illustrate example structures and process stepsfor implementing an enhanced transistor topology enabling enhancedcurrent capability with buried field effect transistors (FETs) formedbelow and beside traditional FinFETs on a bulk substrate in accordancewith the preferred embodiment;

FIG. 6 is a flow chart illustrating example process steps forimplementing an enhanced transistor topology enabling added device drivestrength with buried field effect transistors (FETs) formed below andbeside traditional FinFETs on a bulk substrate in accordance with thepreferred embodiment; and

FIG. 7 is a flow diagram of a design process used in semiconductordesign, manufacturing, and/or test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with features of the invention, a method and circuit forimplementing an enhanced transistor topology enabling enhanced currentcapability with buried field effect transistors (FETs) below and besidetraditional FinFETs on a bulk substrate are provided.

In accordance with features of the invention, process flow issubstantially identical to the existing FinFET process flow with onlyselected layout shape changes. The present invention allows fabricationof buried field effect transistor (FETs) below and beside a FinFET withno traditional landing areas required to fully land the contacts to theFinFET source and drain as the new buried diffusions on either sideadvantageously are part of the landing area.

Having reference now to the drawings, in FIGS. 1-5, there are shownexample structures and processing steps for implementing an enhancedtransistor topology enabling added device drive strength with buriedfield effect transistors (FETs) formed below and beside traditionalFinFETs on a bulk substrate in accordance with the preferred embodiment.

In FIG. 1, there is shown a processing step with a formed FinFETgenerally designated by the reference character 100. The FinFET 100 isformed using traditional FinFET fabrication technique on a semiconductorsubstrate 102. The FinFET 100 includes a gate region 104 formed on agate dielectric 106, a drain region 108, and a source region 110. FinFET100 includes the drain region 108 and the source region 110 that areformed without a dog-bone shaped source and drain. For example, for an Ntype FinFET, the semiconductor substrate 102 is a P-silicon substrate;or alternatively for a P type FinFET, an N-Si substrate could be used.

In FIG. 2, a next processing step generally designated by the referencecharacter 200 provides a blanket spacer 202. The blanket spacer, such asSiO₂ spacer film, is applied or deposited over the FinFET 100 andsubstrate 102.

Referring to FIG. 3, there are shown next doping processing stepsgenerally designated by the reference character 300 to form first andsecond buried FETs generally designated by the reference character 302.The first and second buried FETs 302 are formed in the substrate 102,with the left and right extensions of the FinFET gate 104 acting as thegate of the planar buried FETs. Angled S/D implants, such as ˜45 deg and˜135 deg angled source/drain implants are provided through the spacer202 into the source and drain regions 304. The angled S/D implants areutilized to dope the FinFET source and drain and the new buried fieldeffect transistor S/D diffusions 304. These S/D diffusion areas 304exist on either side of the FinFET drain 108 and source 110 regions andform two planar buried FETs in parallel with the FinFET. The implantedS/D diffusion regions 304 are activated via the same anneals as the baseFinFET device that utilize a conventional or traditional process.Subsequent contacting to the gate of all three parallel transistors ismade via traditional means.

Referring to FIG. 4, there is shown next step generally designated bythe reference character 400 that includes anisotropically etching toremove the spacer from all horizontal surfaces of the FinFET 100 andsubstrate 102 leaving only sidewall spacer 202.

In accordance with features of the invention, the source and draincontacts are one of the greatest advantages of this invention. Notraditional landing areas are required to fully land the contacts to theFinFET source and drain as the new buried diffusion on either sideadvantageously are part of the landing area.

Referring to FIG. 5, there is shown next steps providing circuitstructure generally designated by the reference character 500 thatinclude constructing a respective bar contact that crosses the fin andcontacts all three drains, and another all three sources is constructed.A bar contact 502 to the common drains and another bar contact (notshown in FIG. 5) that crosses the fin and contacts all three commonsources is constructed. Circuit structure 500 nominally requires lesstotal transistor area than a traditional FinFET area and addssignificantly to the total transistor current.

Referring now to FIG. 6, there are shown example process steps forimplementing the enhanced transistor topology enabling enhanced currentcapability via added device drive strength with buried field effecttransistors (FETs) formed below and beside traditional FinFETs on a bulksubstrate in accordance with the preferred embodiments.

As indicated in a block 600, a FinFET is formed using traditionalfabrication technique on a bulk substrate without a dog-bone shapedsource and drain. As indicated in a block 602, a blanket spacer isapplied to the sidewall and horizontal surfaces of the FinFET and thebulk substrate.

As indicated in a block 604, ˜45 deg and ˜135 deg angled source anddrain implants are completed through the blanket spacer and into thesource and drain regions of buried FETs that are formed on either sideand under the FinFET where the gate of the FinFET becomes the gate ofeach of the buried FETs and allows self alignment to the underlyingsources and drains of the buried FETs in the bulk semiconductor. Theimplanted regions are activated via the same anneal or anneals as thebase FinFET.

As indicated in a block 606, anisotropically etching is provided toremove the blanket spacer from the horizontal surfaces of the FinFET andthe bulk substrate.

As indicated in a block 608, a first bar contact to all three drains isconstructed, and another bar contact to all three sources isconstructed. The FinFET and first and second buried FETs are connectedin parallel, having the common source connection and the common drainconnection. The parallel-connected FinFET with first and second buriedFETs enable enhanced current capability, and no traditional landingareas are required to fully land the contacts to the FinFET source anddrain as the new buried diffusion on either side advantageously are partof the landing area with the enhanced transistor topology of theinvention.

FIG. 7 shows a block diagram of an example design flow 700 that may beused for high speed serial link circuit and the interconnect chipdescribed herein. Design flow 700 may vary depending on the type of ICbeing designed. For example, a design flow 700 for building anapplication specific IC (ASIC) may differ from a design flow 700 fordesigning a standard component. Design structure 702 is preferably aninput to a design process 704 and may come from an IP provider, a coredeveloper, or other design company or may be generated by the operatorof the design flow, or from other sources. Design structure 702comprises circuit structure 400 in the form of schematics or HardwareDescription Language (HDL), a hardware-description language, forexample, Verilog, VHSIC Hardware Description Language (VHDL) where VHSICis Very High Speed Integrated Circuit, C, and the like. Design structure702 may be contained on one or more machine readable medium. Forexample, design structure 702 may be a text file or a graphicalrepresentation of circuit structure 500. Design process 704 preferablysynthesizes, or translates, circuit structure 500 into a netlist 706,where netlist 706 is, for example, a list of wires, transistors, logicgates, control circuits, I/O, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign and recorded on at least one of machine readable medium. This maybe an iterative process in which netlist 706 is resynthesized one ormore times depending on design specifications and parameters for thecircuits.

Design process 704 may include using a variety of inputs; for example,inputs from library elements 708 which may house a set of commonly usedelements, circuits, and devices, including models, layouts, and symbolicrepresentations, for a given manufacturing technology, such as differenttechnology nodes, 22 nm, 14 nm, and smaller, design specifications 710,characterization data 712, verification data 714, design rules 716, andtest data files 718, which may include test patterns and other testinginformation. Design process 704 may further include, for example,standard circuit design processes such as timing analysis, verification,design rule checking, place and route operations, and the like. One ofordinary skill in the art of integrated circuit design can appreciatethe extent of possible electronic design automation tools andapplications used in design process 704 without deviating from the scopeand spirit of the invention. The design structure of the invention isnot limited to any specific design flow.

Design process 704 preferably translates embodiments of the invention asshown in FIGS. 1-5, and 6 along with any additional integrated circuitdesign or data (if applicable), into a second design structure 720.Design structure 720 resides on a storage medium in a data format usedfor the exchange of layout data of integrated circuits, for example,information stored in a Graphic Data System (GDS) or GDSII (GDS2),Global Level-1 (GL1), Open Artwork System Interchange Standard (OASIS),or any other suitable format for storing such design structures. Designstructure 720 may comprise information such as, for example, test datafiles, design content files, manufacturing data, layout parameters,wires, levels of metal, vias, shapes, data for routing through themanufacturing line, and any other data required by a semiconductormanufacturer to produce embodiments of the invention as shown in FIGS.1-5, and 6. Design structure 720 may then proceed to a stage 722 where,for example, design structure 720 proceeds to tape-out, is released tomanufacturing, is released to a mask house, is sent to another designhouse, is sent back to the customer, and the like.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

1. A circuit for implementing an enhanced transistor topology enablingenhanced current capability comprising: a fin field effect transistor(FinFET); said FinFET formed on a semiconductor substrate; said FinFEThaving in-line source and drain regions formed without a dog-bone shapeand a gate region formed on a gate dielectric with first and second gateextensions extending past opposing sides of said in-line source anddrain regions; a first field effect transistor (FET) formed in saidsemiconductor substrate beside and under said FinFET and a second FETformed in said semiconductor substrate beside and under said FinFET;each of said first FET and said second FET having buried source anddrain diffusions formed in said semiconductor substrate on the opposingsides of said in-line source and drain regions with angled implants usedto the dope said buried source and drain diffusions and FinFET; and saidfirst and second gate extensions of said FinFET providing a gate of saidfirst FET and said second FET.
 2. The circuit as recited in claim 1wherein said Fin FET, said first FET and said second FET are connectedin parallel, having a common source connection and a common drainconnection.
 3. The circuit as recited in claim 2 wherein each of saidcommon source connection and said common drain connection include a barcontact.
 4. The circuit as recited in claim 1 wherein said semiconductorsubstrate includes a bulk substrate.
 5. (canceled)
 6. (canceled) 7.(canceled)
 8. (canceled)
 9. (canceled)
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 11. (canceled) 12.(canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)
 16. A designstructure embodied in a non-transitory machine readable medium used in adesign process, the design structure comprising: a circuit tangiblyembodied in the non-transitory machine readable medium used in thedesign process, said circuit for implementing an enhanced transistortopology enabling enhanced current capability comprising: a fin fieldeffect transistor (FinFET); said FinFET formed on a semiconductorsubstrate; a first buried field effect transistor (FET) formed in saidsemiconductor substrate under said FinFET and a second buried FET formedin said semiconductor substrate beside said FinFET; a gate of saidFinFET providing a gate of said first buried FET and said second buriedFET, wherein the design structure, when read and used in the manufactureof a semiconductor chip produces a chip comprising said circuit.
 17. Thedesign structure of claim 16, wherein the design structure comprises anetlist, which describes said circuit.
 18. The design structure of claim16, wherein the design structure resides on the non-transitory machinereadable medium as a data format used for the exchange of layout data ofintegrated circuits.
 19. The design structure of claim 16, wherein thedesign structure includes at least one of test data files,characterization data, verification data, or design specifications. 20.The design structure of claim 14, wherein said FinFET, said first buriedFET and said second buried FET are connected in parallel, having acommon source connection and a common drain connection.